OP, I think Y are kind of TA here. She might BTA too, depending on a clarifying question I have: are your family members ok with being deadlifted? Is your gf just sort of ambushing them, tying straps around the group, and getting in a quick set? Or is this something they are participating in willingly? If not, then she is also an asshole. Don't hogtie and orchandle families with out their consent, you know? But I'm guessing they were all fine with it and took it in good humor.

(Sidenote, OP. If you do get your shit together on this, the implication is that your gf is pretty skilled with rope and knots, so think through some of the fun potential applications there! Her shenanigans may have been a hint to you that you were clueless to! Not to overly stereotype, but I find that orcs often prefer to 'show' rather than 'tell'.)

Anyway. Your ego is feeling a little bruised but you need to get through that. Just because she is physically stronger than you doesn't mean you aren't a real man or that you are weak. In fact, I think she is trying to help you with that, if you could see it. Everybody knows you don't play with food in orc households that's ready to eat; you get right down to business. She's trying to bulk you up, my guy, so that you feel more secure about her. She's hoping that one day you'll be strong enough to deadlift her family members, individually at least. So don't be an elf about it, dude. Frankly your gf sounds cool as hell. She didn't break up with you, so this is probably salvageable. My advice is to apologize and try to be a better sport going forward. If you really want bonus points, some time when the two of you are alone, hand her the ropes and tell her you are ready for your deadlifting and see how things go.

Tl;dr YTA, and your gf is clearly dope as hell, so fix it, OP. And then report back.