Ah, got it. I'd at least make an overture to her of telling her this is above & beyond usual and ordinary medical expenses, would like her input, and would like her participation 50%. Give her a report of the options you've looked at. Offer to structure the timing to fit her schedule & financial pressures -- i.e., tell her you won't start until Jan 2013, or you'll start early if it helps with deductibles or unused Section 529 / reimbursement accounts.
Bottom line, is don't assume this won't be brought up some day. This issue isn't worth court costs & lawyer fees. But you have years more to go with your ex, you want three or four things to have to seek "clarification" on should you go back. If your ex genuinely triggers something worth a hearing, this and the other issues you've accumulated are included in the motion, for at least negotiating purposes.
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