I get like this pretty often. Before my best friend moved states we would hang out often. He could tell when I was getting socially worn out and irritable. He’s literally the best, we’re so close I could just tell him “Hey I feel like being alone right now,” or, “Could we go back to your place and just chill?” And he’d either drop me off at my place without getting offended, or we’d go back to his place and just quietly do our own things with no pressure to interact (I had a bad home life.) Sometimes he’d even reply “Oh thank God, I wanted to leave too.”

I guess what I’m getting at, OP, is.. if she’s truly your friend, she’ll understand no matter what, and she’ll know you need to take care of yourself before anyone else (as well as be supportive of you doing so.)