One of my dogs definitely gets exhausted after a lot of boarders or after longer stays. It wears on her to have dogs in her space so frequently, even when she likes them, and it lowers her threshold for her to react negatively to other dogs. When she tells me she needs a break, we take a break. I make sure she gets a say in how often we host dogs because it's her home, too, and it's not worth it to me to continue boarding if it makes one or both of my dogs unhappy.
When a dog (or person) experiences something they find stressful, their body releases cortisol, which is part of the system which regulates the fight or flight response. Even good stress will contribute, like having a long day running and playing with friends. The effects of stressors are cumulative--cortisol takes 24-48 hours to leave the system once the stressor ends, so if your dog finds meet and greets and sharing her space with other dogs stressful, cortisol levels keep stacking up with all the little stressful events, and then her body takes days to return to normal after life returns to normal. This means she will be more and more on edge the more stress she has to experience, and as I'm sure you know from your own experience, the more stress you've already faced, the harder it becomes to cope with additional triggers. Eventually, the smallest thing, something that normally wouldn't bother you, becomes a Really Big Deal. In human terms, you might snap at a friend for making an innocuous comment when you've had a couple bad days at work. Your dog is just the same.
Giving your dog quiet time while other dogs are around, teaching her some relaxation techniques, and taking a few days off from sitting or holding meet and greets when she's telling you she needs a rest will help your dog cope and prevent her from developing bad habits when interacting with other dogs. Also be sure to reward good behaviors when she's greeting and interacting with other dogs to reinforce those pathways and make good interactions her preferred choice. You want her to have positive associations with good behaviors so it's easier for her to choose those behaviors when her fuse is shorter. It's also worth noting that it's really common for dogs to become less social and less tolerant of new dogs (especially if they display any rude behavior) as they age. It's still a good idea to reinforce good manners, but it's totally normal if she seems increasingly less interested in interacting with new dogs as she gets older.