Help with 2 Apple IDs and 2 watches but 1 Iphone

I don't have an iPhone and won't get one until my phone is eligible for upgrade. My sweet girlfriend, who does have an iPhone, bought me an Apple Watch 3 for our anniversary thinking she could use her phone but my Apple ID (I have an iPad) and we could each use our watches with separate IDs and health info. We can't figure out if there's a way to do that, though. I don't care about her phone collecting any of my info or having access to the watch after I get it all set up. I just want it to not have all HER info such as age, height, weight, etc so I can track my own health stuff. Is there a way to do this? Help!