Happy Saturday!
I have to agree with, linette333. Comparing your stride to that of a man, suggesting your gait has changed because you're "older" making it so hard to walk

and then proposing Pilates may "improve your posture" all sound like thoughtless and disrespectful comments to me. Especially given you're recovering from a recent major surgery and through your estimation doing well. With that said, you know your friend, we don't, but I don't like her anyway.
I think your idea of going back to your PT for an objective assessment of your gait and progress to this point is a great idea. That way if anything needs tweaking she can advise accordingly. You didn't mention a limp, but if you do have one, even the slightest, concentrate on heel-toe walking. It does take concentration for many of us because it can feel unnatural. A few months into recovery, even though I was no longer limping for the most part, if I was tired, I'd catch myself slightly limping or someone would ask if I was limping. That is why I am wondering if you were slightly limping.
Many return to Pilates and I don't think it's too soon at three months post op. I'd most likely do one of two things...check with the office of your OS to see if they're are any movements / positions they prefer you refrain from, or at the very least let the instructor know you've recently experienced THR so if there are any positions you need to avoid, they can be modified. I'd take it slow listening to my body as my guide.
Chin up, you are doing well. I hope the rest of your weekend is lovely!
@Calgal