"Have you seen her book?"
On my android phone: if you tap a lesson (like Greeting 1) you get a popup menu. Don't tap 'start' which will take you into the exercises. Above the start button you see a 'key button' on the far right and a 'lightbulb button' to the left of the 'key button'. Tap the 'lightbulb button' to go to the grammar section.
了 is in some of the answers but in others not. I think in this case it means an action that has been completed. 了has several meanings, but commonly it is used for completed actions (but not always in the past).
In English I suggest it could be interpreted as "have you seen her book" - up until that moment in time. So it's a completed action. 了can also be used to bring greater attention to something as well.
Unfortunately it is a bit confusing at first.
As the Chinese is currently written ("你看见她的书了吗？"), we're dealing with sentence-"了", and the difference between this and "过", I think, would be that "过" would connote "ever/yet in general", and sentence "了" would connote being in an immediately relevant state of having recently seen the thing in question and being able to contribute to the search for it.
This sentence brings up at least two issues: whether and how to indicate the past, and what's the difference between看, 见, 看见, etc. Chinese doesn't have tense, it has aspect, which is not the same thing, tricky though it is for us non-natives to understand. The past is not always overtly marked in the verb. It may be clear only in context, or from a time adverb (昨天, 已经, ...), etc., and not just from putting the perfective verbal 了 or the experiential 过 right after the verb. Sentential了 (suggested by a couple of people here), that comes at or near the end of a sentence or clause, is not the same as perfective verbal 了, even though one of its several meanings of uses is to indicate change of state to something different from the past. Here's a link listing a number of different ways to refer to the past in Chinese: https://resources.allsetlearning.com/chinese/grammar/Referring_to_the_past
Various uses of 了: https://resources.allsetlearning.com/chinese/grammar/了
The second point, regarding differences between看, 见, 看见, etc., also connects to the question of indicating the past, because 看见 is a result complement (/complement of result), not simply a semantic melding of 看 look/read and 见 see/meet with. Because there's an indication of the result of an action, there's the implication that the action took place in the past, and lead to the result. Certain adjectives or single syllable verbs (including见 and到) are added a behind a (conventionally matching) main verb to form a result complement. Note that 听见, is a similar result complement in which we can see that 见 in such a construction need not literally mean see. In English, certain adverbs are used to similarly indicate a result: eat up, drink down, polish off, write up. Here are a couple of links about Chinese complements of result: https://resources.allsetlearning.com/chinese/grammar/Result_complements