Hi -- Where religion is involved, a person does not want to compromise. I know -- I'm an Eastern Orthodox Christian, and there are certain times during the year when I fast from meat (Lent, Advent, etc...) -- I have a little bit of a reprieve though -- on Fast days, certain seafood is permissible for us. So, I'm understanding a little of where your sister is coming from. You say she is a sweet person. She probably doesn't want to put you to extra work cooking for her, so she just opens a can of veggie meat. It doesn't sound like she's trying to convert you. Here are a few things I do on Lenten-type days:
For breakfast sometimes I make a "cereal" -- I layer in a bowl: berries, walnuts, hemp seed heats, sunflower seeds, a little ground flax seed, and shredded coconut. I sprinkle with a little flax seed oil, and then pour on a milk alternative (I use a mixture of canned full-fat coconut milk, and unsweetened plain almond milk -- the straight coconut milk is too rich for me). You can also add a few raisins for more sweetness. Then I eat it just like cereal.
Another breakfast that is amazingly good is a green smoothie made with 1 cup cold green tea (just make "sun tea" with 2 tea bags in a quart jar of water -- keep in the fridge), 1 chopped apple, 1 half lemon (pulp scooped out with a grapefruit spoon), and 1/4 avocado. Whir at a smoothie setting in a blender. Then add up to 2 cups greens (spinach is the mildest, but you can use kale, collards, parsley, etc..... even romaine lettuce) Yum! I find if I add the avocado I don't need much sweetener if any -- I used to add truvia, but I find I don't need it any more. My tastes have changed.
For other meals, I like the Shirataki noodles -- you get them at an Asian store. They are made from an Asian variety of yam. They have no calories! (They come in a package with liquid. You drain the liquid, then rinse well, then simmer them in broth for about 10 minutes before adding a sauce. Mark reviewed them and said they were okay -- he didn't particularly like them -- but he doesn't have a weight problem. I think they are great and keep me full for a while.) I like them with mushrooms and marinara sauce. Not much protein so I have some almonds and dark chocolate for dessert.
Also I found a good recipe for a curried sweet potato, coconut milk, and peanut butter soup. You could substitute almond butter for the peanut butter. I've also started to investigate raw eating on lenten days -- there are some good blender soups containing avocados. Also greens are particularly important. Lots of salads and green smoothies.
Personally, I've come to the conclusion that healthy fats are at least as important as the protein or perhaps more important. I try to emphasize avocados, nuts, and olives, on lenten days. Of course, my lenten eating is only temporary. It would be hard to be vegan year round. Anyway, let her eat her thing, and try to emphasize the foods you both have in common. You are both true believers in your own ways of eating, so you probably won't change each other. Finding what you both can eat could be something that could draw you together!
Good luck and God bless!
"I don't know the key to success, but the key to failure is trying to please everybody."