I'm with the gentleman above me on that the sentence looks a tad awkward in writing when it's stripped of any context. One instinctively interprets the verb as the present-tense form of 'read' at first, immediately realising that it doesn't agree with the noun, and then the reader has to make a conscious effort to interpret 'read' as the past-tense verb.
Since the original Russian sentence doesn't contain any indication as to whether mom is still alive or not (unlike the English translation), I think it would make sense to change the default translation to something like 'Mom has always read a lot.'
Not necessarily. In Russian, you'd use the past tense to simply reflect the fact that what you're saying is based on your previous experience, rather than recent observations. Which means that you'd also say "Мама всегда много читала" if e.g. you weren't living with your mum any more, and were responding to someone else's retelling of what she's up to these days.
Russian imperfective aspect is starting to sound similar if not identical to imperfect tense in Romance languages.
In such tenses, this sentence could be translated as:
"Mom always read a lot"
"Mom always would read a lot"
"Mom always used to read a lot"
The one translation which would not be correct for Romance imperfect is "Mom has always read a lot", which is present perfect.
That leads me to wonder if there is any verb combinations in Russian which directly translate the perfect tenses: an auxiliary verb + past participle. I have seen был used as a kind of auxiliary.
There is such a distinction between the ongoing or habitual nature of imperfect tenses and the conclusiveness of the perfect tenses that it seems impossible to me that there's not something like compound tenses in perfective aspect which corresponds to the perfect tenses in Romance languages.
I guess I'll just have to wait and see. Russian is taught very differently from Romance languages.