get a white cloth and see if it transfers with northing on other than water. if it does then rinse with plain water to see whats left, if no transfer, try a M/S on the towel if yes then use that and rinse, if not try other things, start mild and work your way up, and just do small test patches not the whole stain, theres water based solvents, paint removers in fact anything in your arsenal but just be careful and pretest, and remember, very small amounts, your seeing if you get transfer first. if nothing works then its onto reducers but only use if you know what your doing, if not then turn the job down, buy some fake blood and practice. maybe she's got some fake blood left and an offcut of the same carpet, ask her if you can take it home and do some tests.
hope this helps