Agree with Mr. Death. The signs there don't really point to Murphy having moved on for a couple of reasons.
One, in the meta context, we've had an arc from the end of Changes of 'Murphy and Harry are getting into a place to give it a go'. It would be a waste to anticlimactically go "welp, after FOUR books on this arc it's a dead end".
Second, when Harry fantasized about her, she reacted pleasantly and coy. If she'd moved on and had been planning on turning him down, that makes no sense as a reaction from what we know about Murphy. Likewise, as Mr. Death pointed out, her final scene being her making out with Harry enthusiastically makes no sense.
Third, the idea that Murphy would just give up everything to retire and get engaged is an uncharitable one for many reasons. The first is simply that it's well-established Murphy is gunshy about relationships and the idea of getting married after her failed marriage, and it's established it's a part of her hesitance to get into anything serious let alone with Harry. Second, the "Murphy can't keep up" debate is an old one but I'll repeat it: Murphy's in her
forties. Michael was older than her and still active, even while married and having a family. Marcone is also older, iirc, and very involved in things despite not being the person always in the thick of things. Likewise, the presence of people like the Paranet group or even Forthill show there's more to be done than just fight.
And yet, it's always Murphy who gets the "she's too old" measurement.
EDIT:
I mean, do you believe any woman should retire from physically extensive activities or jobs the moment they hit forty?