Sadly, I think there's more precedent too.

ch. 22 much is said to and in front of Fanny “I grant you the name is good in itself, and Lord Edmund or Sir Edmund sound delightfully; but sink it under the chill, the annihilation of a Mr., and Mr. Edmund is no more than Mr. John or Mr. Thomas.

to Edmund
“I mean to be too rich to lament or to feel anything of the sort. A large income is the best recipe for happiness I ever heard of. It certainly may secure all the myrtle and turkey part of it.”
“You intend to be very rich?” said Edmund, with a look which, to Fanny’s eye, had a great deal of serious meaning.
“To be sure. Do not you? Do not we all?”

Mary has consistently spoken openly of marriage as a take-in, a manoeuvring business and that one should make the best monetary connection as possible. She also expects that Henry will "cease to love" and tells Fanny that he might love her nearly forever. I get the impression she doesn't see love in marriage as lasting or realistic at all.

With her aunt and uncle as an example, and then her friend's mercenary marriages, she laments the unhappiness, but seems to see it as inevitable anyway. She just seems to me to be so firm in her thoughts on marriage, that she doesn't expect Fanny to disagree.