Dude, orc culture places a huge emphasis on personal strength and personal improvement. It's been one of their big things going back for centuries. Her displays of strength, whether lifting your entire family at the same time, suplexing ever bigger boulders, or throwing spears through trees, all of those are things she is so proud she is able to do. She is thrilled she can show off those feats of strength to you.

Given your post, she feels that her physical abilities surpassing yours make you feel uncomfortable and is responding in a way that seems entirely logical and consistent with her culture: self improvement. She wants to help you be stronger so you don't feel uncomfortable around her because she loves you. However, you are human. It would take a lifetime of work to ever come close to the feats of physical strength an average orc child is able to achieve. Despite that, and despite having grown up in a culture that massively prizes physical strength, she sees something in you that is more important than bulging muscles. There's something about you that makes her happy. Heck, her family sees it and is happy for their daughter and you.

Let go of your worries about not measuring up physically. It's ok that you're not as strong as she is. Let her know you love her, keep doing what you do, and as always be kind to her and yourself. Relationships across cultures can be difficult, but with love, patience, and communication I promise you two can keep making it together.