I agree with what Ramya and Robbin have said, though I do agree with you that Fanny is a doormat in that she accepts being treated badly and does not complain.

I disagree strongly though that she is martyr, because that implies that she is seeking sympathy while being the cause of her own problems. And that definitely not Fanny. She doesn't seek sympathy, she endures.

It's funny we (at least I) love Lizzie Bennett because of the way she knows just what to say and when to say it. Everyone loves to see the bad guys get their comeuppance, and we love our heroes and heroines that much more when they're the ones to give it to them.

I think you brought up a good point earlier about contrasting her with Mary. Mary is lively and interesting. Just who is the heroine of this novel? Up to this point Fanny has not seemed like someone who is up to job.

In ch 2
There was no positive ill–nature in Maria or Julia; and though Fanny was often mortified by their treatment of her, she thought too lowly of her own claims to feel injured by it.

Ouch! What self esteem this little 10 yr old girl had from being important in her own family was completely pushed out starting with Mrs. Norris' lecture on the way to MP and the treatment from almost everyone thereafter.

So she has accepted her role as companion and servant. She is meek and submissive. The headache for example, I can imagine her head was pounding, but since she is the servant, she goes into the dark corner lays down hoping it will go away, but staying within earshot in case she's needed.

I know religiosity was mentioned and I think of Fanny the meek.
Blessed are the meek, for they shall inherit the earth. Fanny is the definition of meek, will she at least inherit a happy ending?

On a final note,
Fanny's would have been easy to please
ch. 3 “This was so thoughtful and kind!” and would he only have smiled upon her, and called her “my dear Fanny,” while he said it, every former frown or cold address might have been forgotten