I would get your girl on hormonal birth control ASAP. Their protection rates are even higher than condoms, especially if you do it properly and don't miss any doses. Plus, then you don't have to be having sex with a balloon.
If she's worried about remembering a pill she can try the patch (ortho-evra) or the shot (depo-provera). The patch is like nicoderm but you change it once a week, and the shot it one prick followed by THREE MONTHS of completely safe sex
Although of course they won't protect you from STDS, but you already seem to have skipped that part
