Hi Liselott, Congratulations on making it to 100 words! That's an accomplishment! I agree with MamaofWill. Don't worry.
I understand wanting to do it the right way, but it won't cause any complications to show the change in the couplets. I am sure when you speak to her you are not worried about this confusing her in spoken language. So, trust that she will not be confused in written language either. If anything, it will help her to learn the rules of your language quicker and she will be all the more ready to understand what you say and say it herself when she is ready.
It might help her to highlight the parts of the words that are the same with text color. Maybe something like "
grijs" and "
grijze
olifant" I don't think she will be confused if you don't. Babies just accept what you say and show them without asking questions! But, it might help her to recognize the patterns of the language sooner.