Natalie, let the doctors make the decisions...or at least the doctors and Mark. Don't take this on. You already are dealing with more than is comfortable.
Liver patients often have enlarged spleens--how large varies. Mine is somewhat enlarged, but has never bothered me. If it is removed, yes, she would be more susceptible to infection so precautions would need to be taken: Perhaps a mask for her if she is around sick people, and freqent hand washing and use of Purell hand sanitizer for all of you.
Don't let this newest blip on the radar stress you out.
Hugs,
Connie