I agree with the suggestions that you could make up your own concoctions which look custardy and if need be, put them in an empty washed out jar.
I know it's crazy but kids can be creatures of habit and she may be reassured to have it out of the jar! Obviously better to have her eat from a regular kids bowl but one step at a time if need be and keep jar going if that helps get her tastebuds used to something else and then introduce bowls unless you think she'll be ok with bowls in the first place if the food looks appealing!
Sometimes with my kids I will make it look like I'm giving something from my plate when in fact it's from their plate but for some reason my food always looks more appealing than theirs!
They're at the age where I can usually share my food with them but sometimes it's a little too spicey for them so I have to try to make it look like it's mine but actually it's not! Yes you can stand up to them but I think a little bit of subtle substitution works better than creating an neccessary battle.
Kids can be pretty quirky!
But they have very short term memories at this age -you have to ride out any complaints but you can usually break a habit (yours and theirs!) over 2-3 days.
Cheese sauce can look like custard so you could try making that and putting a bit of grated cooked pasta and veggies in it and if need be serve it from a jar!
Or make it look like you're eating it and going to "Share" it with her -kids seem to love sharing food/drinks with their parents.
Another option while trying to break the custard habit is to offer some finger food which she can pick up herself rather than you feeding her. Or get some soft fruit like papaya finely chopped and let her get used to eating it by herself using her fingers.
Sometimes I can get my daughter to try new things if I encourage her to feed herself rather than me try to feed her something that doesn't look familiar. I think children naturally like to pick things up and put them in their mouths so try offering things that she can try to pick up herself -just put it in a plate infront of her on the high chair and let her get on withit even if it gets messy. Grated cheese was an absolute winner for my kids at that age -very easy for them to pick up and eat on their own. From there you can extend the menu. Plus it helps them to be self feeders which is always a bonus!