First, I presume the spouse whom you mentioned is a "non-US citizen" is actually a nonresident alien (i.e. also not a green card holder).  I also assume that there is no §6013(g) election in effect.  If your client intends to elect joint filing, you should assess not only the immediate year's tax impact but also review with them the downstream implications.

In addition to Susan's suggestion, it is possible that your client might be able to file HoH based on §2(b)(2)(B) but the child in college must be a qualifying child who is only away temporarily (intending to return except for the time attending college) and she must have paid more than half the cost of keeping up the home.