Morning ladies

Quick question.

Miss Z has been fully formula fed from about 3 months. No problems at all

However, now that she is nearly 8 months old, she STILL won't take to the next size up from the 0 - 6 month teet/nipple!

I keep trying and she just gags and spits it all out!

So am still using the 0 - 6 month teet/nipple.

Is that okay? Or should I try something else?