Word for "drawing a decisive conclusion about a phenomenon according to specific personal experience"

"Hearsay", besides the legal definition, describes the scenario you described:

1. Unverified information heard or received from another; rumor.
2. Law Evidence based on the reports of others rather than the personal knowledge of a witness and therefore generally not admissible as testimony.

From the freedictionary.com

This Wikipedia article calls it Hasty generalization, but if I were A in OP's example I'd say...

You can't generalise from the particular.

I don't understand why OP says his example is "not only generalization", since that's precisely (and only) what it is. Which arguably makes the question itself pointless, but I'm posting this answer because future visitors might find it after searching for words in the question title.

This is similar to the post hoc ergo propter hoc fallacy: basing a conclusion on a single instance. It doesn't matter whether it's true (it's true that the woman in the OP's example sentence found it not user-friendly), false (Reagan's "welfare queen"), or merely hearsay. A single instance of event A followed by event B doesn't prove anything: it merely illustrates a correlation or coincidence.

It's also called "the fallacy of anecdotal evidence" and "the cherry picking fallacy".

The word you are looking for is anecdotal.

Anecdotal (adj): (of an account) not necessarily true or reliable, because based on personal accounts rather than facts or research.

Example: Historic accounts of this era give no indication of any negative impact to fish populations and in fact, anecdotal accounts reflect quite the opposite.

[Lexico]