I think Richard knew Monica as a child a bit, but she didn't register on his radar as she was a daughter of a mate. And no, he didn't recognise her as an adult in her late 20s, as she was a child when he last saw her. I wouldn't recognise the children of people I knew 15 years back, who are in their 20s or early 30s now.
Also, Monica was quite fat as a child/young teen if you remember, and looked quite different after losing 70 pounds. If you recall, Richard was shocked when he realised who she was.
I know several girls who lost weight at 16-17 y.o. (like 40 to 60 pounds,) and they were not only unrecognisable to when they were a fat child/young teen, but they were also much more attractive to men.
Including me. In my teens, I was 12 and a half stone, and 3 to 3 and a half stone overweight, (and that was classed as quite fat some 30+ years ago.) I lost about 40 pounds, (so about 3 stone,) and looked completely different.
I also dressed differently, had my hair cut and styled, and looked much better. At 12 and a half stone I didn't care what I looked like, because I was fat and therefore unattractive by default (according to society and everyone who called me a fat cunt.)
About a year after I lost the weight, (when I was 18,) a lad from school who was 2 years older than me, and used to call me fat-tank, whale blubber and 'the blob' was on his stag night, and started hitting on me. He didn't recognise me, and when I told him to shove off, he said 'you don't know what you're missing!' I said 'I know your fiancee Kelly, and I will tell her you've been letching over me.'
Long story short, he wanted to know who I was, and my mate said 'it's foxy from school.' He looked shocked and said 'oooh, you should have lost that weight years ago, you're way more fuckable now.' 
Wow, if I had lost weight YEARS ago (I was only 16-17 when I lost it by the way,) I could have hooked HIM. What a loss THAT was.
NOT!!!
Unsurprisingly, the marriage lasted 3 years. He kept cheating on her. Shocker. I wish I had told Kelly he had tried it on! Bet she wouldn't have believed me anyway though! 