help with iMovie or similar app

Hello,
I have gotten decent with audio editing on the iPad pro using Hokusai. I produce radio programs, and other radio related audio, such as station ids, sweepers, etc. One of the programs that I produce is for a lady from Puerto Rico who sends me her audio via whatsapp. It’s a spoken word program only, so I take her audio, throw on a program intro, outro, and some background music, and done. Pretty easy stuff.
So, what I want to turn around and do with this, in addition to broadcasting on my online radio station is to make a video with it, combining that audio file done in Hokusai, exported to m4a, with an image of the person speaking, which would last the duration of the whole audio file. There is already a site I use to do that, and it works okay, but it is very very slow. Also, I would like to perhaps add some opening titles to the video, and put her contact info on screen at the end, which I can’t do with that site. I figured something like this could be done in iMovie on the iPad, but have never used the app, and have no idea where to even start. If iMovie won’t work for this, is there another free app that will? Also, a walk through on how to go about this using said app on the iPad would be much appreciated. We’re not talking advanced edits or anything crazy, just the audio track, image, and on screen text throughout the video.