It sounds like she may be contracting a UTI or bladder infection. Which can become common if sex is rough or theres to much friction. If the problem keeps occuring after sex, I would suggest she go to a doctor or the walk in clinic and have it checked out.
Spermicides can be useful for added protection. Although I would be careful with it since spermicides can cause iritation in the vaginal region as well.
Since there already seems to be irritation I would switch to lubed condoms without spermicide.
There has also been alot of controversy over the Spermicide Nonoxynol-9 which is used in most condoms that have spermicide. Heres a link for more information on Nonoynol 9 and its effects. [URL=http://www.safer-sex.co.uk/health/nonoxynol-9.htm]LINK[/URL]
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May not be on LF as much, due to unforeseen circumstances.
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-Fawn