How many ways are there to position yourself to have intercourse? There are different ways to engage in oral stimulation. There is nothing in the rule book that states swallowing or deep throat or letting semen fly inside the mouth is mandatory.
Many women will engage in oral stimulation yet not let a man ejaculate in her mouth, swallow semen, etc. Whatever her limitation is, we guys must abide by her decision.
There is an article on all this listed in the Index. I suggest that both of you read it because she may not know how to handle semen when it is ejaculated. If she reads the how-to information she may very well like full blown oral stimulation after learning how to accomplish the act. If she decides not to do it there is no reason why the two of you cannot enjoy oral stimulation up to the point of ejaculating inside w/o swallowing, or, up to the point where you ejaculate elsewhere.
So, I encourage the two of you to read the article:
How Do I Get Him/Her to Orgasm From a Hand/Blow Job?