I once did a tour of my country with an American friend. I hadn't seen her in a while and was really looking forward to it. I even worked out a whole plan of where to go and what to do (and OKed it all with her) so we could fit in as much as possible. The first week was so great and we were really bonding. Then we gave a Canadian guy that we met in the hostel a ride, which then ended up him spending the next 2 weeks travelling with us. He was a cool guy and ordinarily I would have rather liked him, but the two of them ended up as thick as thieves and I was left out. She is quite a impressionable person and was completely taken with his zen-ness, and worldly knowledge and experience - and it bothered me how much she worshipped everything he said (and a few of his ideas I thought were ridiculous). He also kept questioning the plans I'd made and undermining my knowledge of places/things in joking ways (not a good thing to do to someone with a 5 wing ). I found myself becoming rather stubborn, irritable, pedantic and disagreeable towards them - basically textbook e4 disintegration to e1
Now, I'm TOTALLY NOT the jealous type. I mean, I never get jealous. But it felt like he was pushing in on and disrupting the time I had been looking forward to spending alone with my friend. I had built up the whole thing in my mind, so my disappointment was all the more. And I knew I was being grumpy and ridiculous but I couldn't stop myself. I'm actually kinda embarrassed about some of it but I never said anything to my friend about it.
I know this isn't exactly the same circumstances, nor did I react in the same way as your friend, but perhaps it is a similar case. Maybe she just wanted to spend time with you and felt like your boyfriend was in the way, and then got in a bit of a grump about it. If that's the case then it isn't a big deal. She's probably over it and feels a bit stupid about it.