The woman, known only as ‘WinterIsHereJon’, took to Mumsnet to ask whether it would be acceptable to change her honeymoon plans so that she wouldn't run into her "difficult" mother-in-law.
The bride-to-be is getting married later this year and had planned to spend her honeymoon in the Caribbean island of St Lucia, followed by a few days in the US.
However, her plans have been interrupted by her mother-in-law, who has booked herself into the same resort at the same time as the newlyweds.
Her partner’s mother stayed with them during Christmas and was involved in their honeymoon discussion.
"She was here over Christmas and was involved in the discussion," the bride explained on Reddit.
"Up until now, she has always expressed a dislike of long haul holidays and 'would never go on one'. We were planning a trip to the Caribbean, with a few days in the US on the way back; she thought we could have a nicer holiday in Cyprus."
The bride explained that the couple are limited on dates that they can take off, so they told the mother-in-law which dates suited them best, as she offered to take care of the children while they were away.
She added: "Fast forward to last night and she's posted on Facebook that she's booked a holiday to the same chuffing resort she knew we were looking at. Worse than that, the dates overlap so she'd be there for the first few days of our honeymoon.
"She's making out like it was a pure accident but I really don't feel that it is."
Her mother-in-law has also suggested that the trio head out for a family dinner on their first night on the island.
Mumsnet users responded with empathy and encouraged the bride-to-be to find alternative accommodation.
One user said: "Your future MIL does not understand that her umbilical cord has been cut a long time ago..."
While another added: "I wouldn't be changing my plans at all. I'd be telling your fiance to tell his bats*** mother to cancel her holiday or they'll be no wedding. Put your foot down now or this craziness will continue forever."