Hi Carolyn, thanks for your initial advice! Here's my EtreCheck report:
EtreCheck version: 3.0.2 (306)
Report generated 2016-08-25 01:14:41
Download EtreCheck from https://etrecheck.com
Runtime 7:07
Performance: Below Average
Click the [Support] links for help with non-Apple products.
Click the [Details] links for more information about that line.
Problem: Computer is too slow
Hardware Information: ⓘ
MacBook Air (13-inch, Late 2010)
[Technical Specifications] - [User Guide] - [Warranty & Service]
MacBook Air - model: MacBookAir3,2
1 1.86 GHz Intel Core 2 Duo CPU: 2-core
4 GB RAM Not upgradeable
BANK 0/DIMM0
2 GB DDR3 1067 MHz ok
BANK 1/DIMM0
2 GB DDR3 1067 MHz ok
Bluetooth: Old - Handoff/Airdrop2 not supported
Wireless: en0: 802.11 a/b/g/n
Battery: Health = Replace Soon - Cycle count = 1317
Video Information: ⓘ
NVIDIA GeForce 320M - VRAM: 256 MB
Color LCD 1440 x 900
System Software: ⓘ
OS X El Capitan 10.11.3 (15D21) - Time since boot: about one day
Disk Information: ⓘ
APPLE SSD TS128C disk0 : (121.33 GB) (Solid State - TRIM: Yes)
EFI (disk0s1) <not mounted> : 210 MB
Untitled (disk0s2) / : 120.47 GB (27.95 GB free)
Recovery HD (disk0s3) <not mounted> [Recovery]: 650 MB
USB Information: ⓘ
Apple Inc. BRCM2070 Hub
Apple Inc. Bluetooth USB Host Controller
Apple Inc. Apple Internal Keyboard / Trackpad
Apple Card Reader
Apple Inc. Built-in iSight
Gatekeeper: ⓘ
Mac App Store and identified developers
Kernel Extensions: ⓘ
/Library/Extensions
[loaded] com.sophos.kext.oas (9.5.50 - SDK 10.11 - 2016-08-24) [Support]
[loaded] com.sophos.nke.swi (9.5.50 - SDK 10.11 - 2016-08-24) [Support]
/System/Library/Extensions
[loaded] com.globaldelight.driver.BoomDevice (1.1 - SDK 10.9 - 2016-08-01) [Support]
System Launch Agents: ⓘ
[not loaded] 7 Apple tasks
[loaded] 148 Apple tasks
[running] 56 Apple tasks
[killed] 25 Apple tasks
25 processes killed due to insufficient RAM
System Launch Daemons: ⓘ
[not loaded] 46 Apple tasks
[loaded] 154 Apple tasks
[running] 73 Apple tasks
[killed] 15 Apple tasks
15 processes killed due to insufficient RAM
Launch Agents: ⓘ
[loaded] com.oracle.java.Java-Updater.plist (2015-09-29) [Support]
[running] com.sophos.uiserver.plist (2016-08-24) [Support]
Launch Daemons: ⓘ
[failed] com.adobe.fpsaud.plist (2016-04-16) [Support]
[loaded] com.oracle.java.Helper-Tool.plist (2015-09-29) [Support]
[running] com.sophos.common.servicemanager.plist (2016-08-24) [Support]
[running] com.trusteer.rooks.rooksd.plist (2011-08-21) [Support]
User Launch Agents: ⓘ
[running] com.amazon.music.plist (2015-05-25) [Support]
[loaded] com.bittorrent.uTorrent.plist (2015-11-20)
[failed] com.facebook.videochat.[redacted].plist (2014-08-11)
[loaded] com.google.keystone.agent.plist (2016-07-12) [Support]
[running] com.spotify.webhelper.plist (2016-08-24) [Support]
User Login Items: ⓘ
Flux Application (/Applications/Flux.app)
iTunesHelper Application Hidden (/Applications/iTunes.app/Contents/MacOS/iTunesHelper.app)
Dropbox Application (/Applications/Dropbox.app)
Spotify Application Hidden (/Applications/Spotify.app)
Internet Plug-ins: ⓘ
JavaAppletPlugin: Java 8 Update 71 build 15 (2016-01-29) Check version
FlashPlayer-10.6: 21.0.0.226 - SDK 10.6 (2016-04-21) [Support]
QuickTime Plugin: 7.7.3 (2016-02-26)
Flash Player: 21.0.0.226 - SDK 10.6 (2016-04-21) Outdated! Update
Default Browser: 601 - SDK 10.11 (2016-02-26)
Google Earth Web Plug-in: 7.1 (2013-07-12) [Support]
AmazonMP3DownloaderPlugin101749: Unknown
iPhotoPhotocast: 7.0 - SDK 10.8 (2013-09-15)
3rd Party Preference Panes: ⓘ
Flash Player (2016-04-16) [Support]
Java (2016-01-29) [Support]
Rapport (2011-08-21) [Support]
Time Machine: ⓘ
Time Machine not configured!
Top Processes by CPU: ⓘ
99% Google Chrome Helper(20)
6% WindowServer
4% kernel_task
2% hidd
1% SophosScanD
Top Processes by Memory: ⓘ
1.14 GB Google Chrome Helper(20)
496 MB kernel_task
156 MB Google Chrome
111 MB mdworker(8)
98 MB SophosScanD
Virtual Memory Information: ⓘ
22 MB Free RAM
4.23 GB Used RAM (515 MB Cached)
510 MB Swap Used
Diagnostics Information: ⓘ
Aug 25, 2016, 12:58:40 AM /Library/Logs/DiagnosticReports/_2016-08-25-005840_[redacted].crash
???
Aug 24, 2016, 02:42:03 PM /Library/Logs/DiagnosticReports/SophosWebIntelligence_2016-08-24-144203_[redact ed].crash
/Library/Sophos Anti-Virus/SophosWebIntelligence.bundle/Contents/MacOS/SophosWebIntelligence
Aug 24, 2016, 02:13:26 PM /Library/Logs/DiagnosticReports/SophosWebIntelligence_2016-08-24-141326_[redact ed].crash
Aug 24, 2016, 12:39:47 PM /Library/Logs/DiagnosticReports/SophosWebIntelligence_2016-08-24-123947_[redact ed].crash
Aug 24, 2016, 12:15:58 PM /Library/Logs/DiagnosticReports/SophosWebIntelligence_2016-08-24-121558_[redact ed].crash
Aug 24, 2016, 10:41:19 AM ~/Library/Logs/DiagnosticReports/Preview_2016-08-24-104119_[redacted].crash
com.apple.Preview - /Applications/Preview.app/Contents/MacOS/Preview
Aug 24, 2016, 10:40:15 AM /Library/Logs/DiagnosticReports/deleted_2016-08-24-104015_[redacted].crash
/System/Library/PrivateFrameworks/CacheDelete.framework/deleted
Aug 23, 2016, 05:15:56 PM /Library/Logs/DiagnosticReports/SophosWebIntelligence_2016-08-23-171556_[redact ed].crash
Aug 23, 2016, 05:07:56 PM /Library/Logs/DiagnosticReports/SophosWebIntelligence_2016-08-23-170756_[redact ed].crash
Aug 23, 2016, 05:05:47 PM /Library/Logs/DiagnosticReports/SophosWebIntelligence_2016-08-23-170547_[redact ed].crash
Aug 23, 2016, 04:46:16 PM Self test - passed
Aug 23, 2016, 03:59:58 PM /Library/Logs/DiagnosticReports/SophosWebIntelligence_2016-08-23-155958_[redact ed].crash
Aug 23, 2016, 12:09:30 AM /Library/Logs/DiagnosticReports/SophosWebIntelligence_2016-08-23-000930_[redact ed].crash
Aug 22, 2016, 11:05:25 AM ~/Library/Logs/DiagnosticReports/Preview_2016-08-22-110525_[redacted].crash
Aug 22, 2016, 10:42:08 AM /Library/Logs/DiagnosticReports/SophosWebIntelligence_2016-08-22-104208_[redact ed].crash
Aug 22, 2016, 10:39:20 AM /Library/Logs/DiagnosticReports/Adobe Photoshop Elements_2016-08-22-103920_[redacted].cpu_resource.diag [Details]
/Applications/Adobe Photoshop Elements 8/Adobe Photoshop Elements.app/Contents/MacOS/Adobe Photoshop Elements
Aug 22, 2016, 10:30:36 AM /Library/Logs/DiagnosticReports/SophosAutoUpdate_2016-08-22-103036_[redacted].c rash
/Library/Sophos Anti-Virus/SophosAutoUpdate.app/Contents/MacOS/SophosAutoUpdate