One contact green not blue in messaging

I have an iPhone and so does my friend, but when I text her it sends as a text message and not an iMessage. We both recently got the ios13 public beta and ended up deleting it because we thought that was the problem. Two days later our texts are still sending as text messages. We've tried to turn off iMessage shut our phones off and turn it back on and turn iMessage on again, but it's still not working. This is only with her contact and we both have internet and unlimited data. Help?

Try the following

1. What colour do you see when the that person sends you text. If it is green then they need to activate iMessage with their new number.
2. Send a text to them by directly entering their phone number on a new message thread. It should be blue if the iMessage is activated on both iPhones
3. Send a text to him by directly entering their email ID on a new message thread. It should be blue if the iMessage is activated on both iPhones
4. Do not text using old conversation thread.