1. The problem lies in your mother-in-law's house.
Her computer has a virus or rogue plug-in, which takes up a lot of network speed. Liaoyang cable broadband network speed is very good, so the video will not get stuck.
3. Did she use Thunder or BT to download anything when chatting with you in video? If not, please ask someone to go to her house to check her computer and make the computer system better. It should be no problem.