It depends on what the DOM is on her seat. The manual was revised in April 2008 and the new manual clearly states that less than 45* is allowed for older children. The older manuals did make it sound like the 45* was required, however, this is false.
Maybe refer her to the current manual?
(Although the new manual so many times states the 32" limit, that if she isn't already aware of the 1" from top of shell allowance and the whole issue, it may be better to not direct her to the new manual as it'll open a whole other can of worms... Dumb Britax and their overly conservative interpretation of TC regulations.
I'm still mad they didn't take the opportunity to bring the BLVD in without a fixed height limit and didn't rate it higher than 30lbs rf'ing...)
As long as the seat isn't over-reclined, there is no harm in her keeping it at 45*. It's just not necessary & increases the risk of over-rotation in a serious collision.