Thanks for the chapter!
LN explains things better. The thing about crossing North Mountains being impossible is because it's currently Autumn which is when monkey type monsters group up and actively hunt for their favorite prey, humans, to stock up for the winter. So waiting for winter would be safer because could run into a group of monsters numbering anywhere from ten to one hundred. Also, all that "We can if you're not with us" garbage from the party is to avoid their responsibility to her. In LN current location would take a few months to return her to her home town and group would be obligated to escort her there if fire her or kick her out of party or risk getting in trouble with the guild or the party losing its prestiege. However, if she leaves of her own volition then the party not responsible and could just say fare thee well with no other actions and she'd have to make her own way back without their help.
As for the whammy Gran is putting on her don't know much about it since from her POV and hasn't realized being mentally manipulated. Usual pros and cons of ability like that, (whether a skill, charm, mental manipulation magic, etc.) is that the stronger the person's will and more resistant toward orders they are the weaker the hold. Hence why they're always putting her down so she'd be more susceptible. Since others seem to know about it likely not being influenced or it might have restriction of only working on the opposite gender so Gran might only be able to enspell her. Not enough info to determine whether Lize has been bespelled also or able to resist it due to protection of spirits. Also, whatever Gran doing to MC usually only lasts a short time unless stacked up and recast within a certain time limit along with the effect getting stronger and able to grab a tighter hold of victim's mind the longer and more often it was cast without any breaks. For MC, sounds like the party emotionally abused and Gran always whammied her without breaks for about 2 years.
Kind of wonder why picked her rather than someone from a guild based off of rumors that may or may not have been true. Although probably figured it'd be a a windfall in that if as skilled as rumors said she'd be a benefit, was in Gran's strike zone so could be charmed, village would hardly be able to make much of a protest of her leaving as opposed to someone with connections in a big city guild, and could work her hard while keeping her share of experience and income for themselves. Personally, think the talk about subjugating monsters near the village was a sham to lower village's guard, make them seem good natured, and able to grab MC with little trouble. Hope the party gets what's coming to them with interest. Although don't have enough info on Lize to tell if she's been charmed too, cut from the same soiled cloth as Gran and rest of party, or a bit of both. Guess will just have to keep reading.