I just mixed up two batches of marshmallow fondant. In the first batch I completely forgot to add in the 1/4 cup shortening. In the second batch I remembered it after I had melted the marshmallows and just melted it and added it to the mixture in the mixer. So I have two questions that I need to resolve in the next hour: 1) Can I work the shortening into the first batch after the fact? and 2) Will the second batch be ok? Thanks for your help in advance.

Personally, I've never seen a MMF recipe that calls for mixing the shortening into the mixer... it's used for coating the mixer bowl, microwave bowl, countertop, and your hands.

Yes, you could work it in after the fact, but I wouldn't bother unless it's needed to help prevent it from sticking. Also, if you're mixing/kneading both batches together, I wouldn't add the shortening until you know if it's needed.