Q: Text someone with same Apple ID

No. If you text her it will send the message to both devices with the same Apple ID. Why don't you just set up a new Apple ID for her?

GB

Yes it will work, you can share an ID for purchases and have separate IDs for iCloud.  The 2nd ID for just iCloud (i.e. iMessage and FaceTime) does not have to have a credit card associated with it:

Create an iTunes Store, App Store, or iBooks Store account without a credit card or other payment method - Apple Suppor…

So if you already have an ID for purchases, set up a 2nd ID just for your sister's iMessage and FaceTime.  She'll have to sign out of iCloud if she's signed in under the ID for purchases, then sign back in using the new ID.

Or, use the same ID for everything but set up her iMessage and FaceTime to use a different email address than the ID you're using, you don't have to use your Apple ID as a point of contact for these services.

You don't have to have her pay for all of the apps you already paid for. You both can use the same Apple ID for the iTunes & App Store, but she should set up a separate iCloud account for Messages, FaceTime, Mail, etc.

To do that, on her phone go to Settings>iCloud, and click on Create a new Apple ID. You can then put in any name you want for the email address (as long as it is not already being used), and it will create an iCloud.com address for her that she can use for Messages, FaceTime, Mail.

Cheers,

GB

You should also look into Family Sharing which will allow you to share content while still maintaining separate Apple IDs.