A few things here to verify. First off, does she actually work the days you are asking her to go with you? If the answer is no, then no covering lost wages.
Does she have to buy things to go on the trip. Extra outfits, get a passport, etc. I usually pay for those if it's out of the ordinary. If we are doing one fancy dinner and she wants a new dress we can talk about it. Lingerie and sex toys, hell yes.
You are already paying for everything. Travel, hotel, food, entertainment, etc. I had a SB that wanted double her normal allowance per day we were together for a trip. I said no. She wasn't working so it's not like she was losing income. I had another that just asked that I buy her some nice gifts while we were out. Perfect.
Make sure she understands you want her to go with you. You do not need her to go with you. She does not have GPS.
Current main SB and I are making travel plans where she does not miss any work or school. All she asks is her typical allowance plus some gifts and to pay for anything she needs to buy to take with us. Perfect for us. She already knows we will eat well, stay in great hotels and have a lot of fun. Why ruin it being greedy?