latam – Second leg of a multi leg flight cancelled by airline – what are my rights / options

My daughter booked a oneway Paris -> Sao Paulo -> Bogata flight with carrier LATAM though govoyages.com. The flight is in 4 weeks.
A few days after booking she was notified by govoyages.com that the Sao Paulo -> Bogata leg has been canceled by LATAM. Govoyages just said the leg is canceled and they are pursuing reimbursement with LATAM. They didn’t offer any alternative flights or any further information. There phone line suggest the reimbursement processes could be very long e.g. 6 months.
Looking at flight options to replace this leg is looking complicated.

What are our rights with regard to:
a. Cancelling the first leg with either govoyages or LATAM (and hence effectively the whole trip) so we are able to rebook a NEW Paris -> Bogata rather than scraping round for a Sao Paulo -> Bogata leg which will like cost as much as the whole trip. OR
b. Getting a replacement Sao Paulo -> Bogata leg offered by LATAM to replace the flight they canceled.

Currently we have half a flight which is pretty useless. Any advice much appreciated.