Did she even respond to your original request or did she just ignore it with her "counter-proposal"?
If she didn't specifically reject your request (whatever her reasons might have been) would it be appropriate to respond merely by saying something along the lines...
B,
S12 and I want to be together during these last few nights before he heads off to school. S2 is very dear to S12 and we hoped you would be willing to let S2 stay with us Friday night so the two boys could spend some more time together with me. Granted, your suggestion could achieve the end of them being together, but if they are to be able to spend Friday night together, S12 wants it to be with me. Please consider this request in light of S12's desires. Because this is important to him and to me, I would be happy to have S2 spend an extra night or two with you if you would be so willing.
C
Again, I'm not completely versed in the nuances of your discussions with her, but I inferred from your description that she may have ignored your request and just tried to replace it with her own. I would have trouble addressing her question unless she's first answered yours...
-AlexEN
New: What a Weekend
H-48 WAW-49 M-22 S-14,9 D-11 EA disc.-11/07 PA disc.-3/08 EA2?-6/08 to ?