Just wondering if anyone has dealt with this situation and advise on what to do?

I have a DCM who is a teacher so knowingly she doesn't need care march break, extended christmas, and the summer vacation. This mom also takes a lot of time off work during the school year and keeps her child home with her. often 1-3 Fridays a month. I have had them as a clint since their child was 11 months, the child is now 2. When i first signed them on, my contract stated that i did not charge for days not in care. All other parents had the same contract and limited their time off out of respect for the business, no problems there. After the first year I revamped my contract to allow for 15 "free days" within the year of their contract to use at their own discretion. This was mainly because of this specific DCM taking so much time off and only allowing so many "free days". well within 2 months of care back in September she used up almost all of her 15 days. This left her with no more for extra christmas (I take my vacation from Christmas -New years) or the upcoming march break. She understands she must now pay for march break and any other days her child is not here. (a weekly conversation is had accusing me of being unfair and that it makes no sense to charge when he is not in care) I have tried to be reasonable with time off days etc and no other DKP's even use up all their allotted days off within their contract term. I tried to explain to her that they purchase a "spot" that is for them at a weekly cost. I can not fill his spot when he is not here on a "tell me that morning he won't be here" scenario. I tried again to explain it is like a gym membership (maybe i'm wrong in this explanation, but anyway) you pay a monthly fee non dependant on if you use it or not. thats the contract. I feel like i've been fair in my 15 days unpaid, to use how ever they want.

so the kicker.....I told her when she returned this past September that i could not hold their spot over the summer (2015) for free, but that i was willing to reduce their fee to half the daily rate over the summer to hold his spot for next September. She was obviously not impressed by this and said that they were not willing to do that and they would just wait and see if the spot is still available in September. So I went ahead and posted his spot to find another client. Well, I found one! I let her know (out of respect) that i had some interest in the spot and that they might want to start looking for new care for September. They back tracked and now say they are willing to pay the half rate to hold his spot. should I say no to this new client or give priority to the existing one even tho i will loose money taking only the holding fee? i'm frustrated!