Usually, if a F&F is refused, the IVA is allowed to continue on it's merry way, as before. However, if the terms of the offer are such that you say, or imply, that you are making the f&F because you cannot afford to continue the agreed repayments then the natural progression, if the offer is refused, is for the IVA to fail on the grounds that you cannot make the payments.
I would be inclined to speak to the IP, before signing the variation proposal, and ask that a clause be built in to the offer along the lines of "Should this offer be rejected by creditors, then the IVA will continue under the already agreed, pre-variation proposal, terms."
Also ask her line of thinking in making that comment --- it could be that the existence of your property as an asset, albeit excluded, could tip creditors into refusing and asking for BR. However unlikely, it is her duty to warn you of the possibility and none of us here are able to give qualified advice.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014