Best water bottle for bed-bound elder who chews through silicone mouthpieces?

The short of it is: We are searching for a water bottle that can be left in the "open" position without leaking when placed on its side, but the mouthpiece has to be strong enough to withstand an adult attempting to bite through it with their very strong, healthy teeth.

The long story: My MIL is a stroke patient, and is mostly bed-bound in a care facility. She's been using a Camelback kids sized water bottle that has a silicone mouthpiece that you bite on to open the top in order to drink out of it. That top works great for two reasons, one she doesn't have to manipulate the top to open it, and two when she leaves it laying on the bed next to her, it doesn't leak, or at least doesn't leak enough to noticeably wet the bed. However recently she has started biting through the middle of the mouthpiece, which creates a choking hazard. We can buy replacement mouthpieces, but she's starting to bite through them much faster than before, like once a week versus 1-2 months, and we can't be there every single day to monitor this because occasionally we like to take a vacation out of town for a few days. Also we can't rely on the nursing staff to catch it either because they're often overworked and not able to pay attention to details like that. Wondering if anyone has a ready solution before I spend a few hours and some $$$ researching a better solution?