My younger sister has stronger legs than me and uses them to beat me up. How can I counter this?

So I’m 25. She is 18. Yet she has stronger lower body than me. We wrestled at Christmas and and I pinned her down cos my upper body is stronger. But what I didn’t realise is that her lower body is strong and she wrapped her thighs around my waist and squeezed until I had to tap. We have wrestled a few more times after that and a similar thing keeps happening but I have no idea how to break out or counter this lock. Any idea or advice. Thanks
My younger sister has stronger legs than me and uses them to beat me up. How can I counter this?
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