Christine's use of the word "incursion" there was likely a pun -- i.e. a play on words -- rather than something meant to be taken seriously.
Earlier in the film, it was explained that the word "incursion" refers to the destructive collision of two universes:
838 REED RICHARDS: An Incursion occurs when the boundary between two universes erodes and they collide, destroying one or both entirely.
However, this isn't the only definition of the word. In the real world, it can refer to one simply entering an area where they're not supposed to be.
From the Collins Online Dictionary:
- COUNTABLE NOUN
If someone or something enters an area where you would not expect them to be, or where they have not been found before, you can call this an incursion, especially when you disapprove of their presence.
[formal]
Traditional crafts remain remarkably unchanged by the slow incursion of modern ways.
...her disastrous incursion into the property market.
She and Strange were talking about the possibility of him taking her to his universe, where she isn't normally supposed to be, so it seems more likely that she was referring to that, rather than the actual destruction of his universe.
Also, I think the underlying point she was making is that it was a shame she couldn't visit his universe with him, as they could've had a good time together.
It may or may not also have been a double entendre alluding to the prospect of them engaging in sexual intercourse with one another, which is potentially what would've happened if she'd gone with him to his universe and spent a significant amount of time with him.
