Honestly, it sounds like you're overreacting and perhaps even paranoid.
Nothing that you've described about her play is suspicious at all. Most people play this game very casually and don't treat it like a Scrabble game where plays are made within a few minutes. In fact, I'd be much more suspicious if the person I was playing was constantly playing high scoring words within minutes (especially ones that build on to my last play, since they couldn't have known they could play it until after I made my move). I would suspect use of a cheat app, in some cases.
I don't know why you would be so worried about her consulting a dictionary. Truth be told, she could accomplish the same result by testing to see if a word was a word by trying to play it and see if the game allows her to play it. It's cheap, sure, but I wouldn't call it outright cheating. As for consulting other players... I don't think people who are cheating would want other people to know they're cheating. Bringing in an outside party seems highly unlikely.
However since your thread is called "How to detect cheaters", I have come up with a few things that I tend to look at before I dare throw the "C" word around.
The easiest way for me to detect cheating is not to look at the word the person played, but to look at the letters he/she played.
There are two types of cheaters that can be caught, in my experience.
i) Type I: The players who use anagram websites to come up with outrageously obscure (yet very low scoring words). I play people occasionally who consistently play words like "DYNODE" for 11 points, when they could have played "YO" for 24. When I see this happen consistently, I automatically think they're cheating but too stupid to use strategy to cover their tracks. These players don't understand how the scoring of the game works and think if they come up with some really long, unusual word, they will somehow be endowed by the Words With Friends gods with some uber score despite the fact that their word doesn't hit any multiplier squares. I don't even bother to call these players out on anything since I usually beat these people by 300 points anyway.
Type II) The player who uses a website or an app that computes the highest scoring word is the more dangerous type. Sometimes, however, I can tell they're using one when they play a long word and I have a good read on what their tiles are and the silliness of the move (despite it being a high scoring word.) For example, if I saw a player make a 6 letter word like CUPIDS for 35 points that sets me up for the triple word, when they could have played CUP for 33 points in a different area that wouldn't set me up for the triple word, I'd automatically be a little suspicious. Sometimes players who use these sites are too stupid to think about good strategy, and all they see is CUPIDS is at the top of the list of high scoring words, so they go for it. A one time offense is, of course, forgivable. But a player who consistently makes high scoring plays that demonstrate absolutely no understanding of strategy is a serious red flag, because a player who was intelligent enough to see these high scoring plays would likely know it's worth it to sacrifice the extra point or two if it means not setting your opponent up for a huge play.
By the way, another red flag for a player likely using a cheat app is when they are very frequently making high scoring words, yet often tacking S's onto words for an additional one point or two points for their play. Most experienced players would know that an S is much more valuable than the extra 1 or 2 points and that it makes much more sense to save it. Cheat apps (and often the players who use them) don't consider this when they form the highest scoring word. (Be careful though, sometimes people dump an S because they have 3-4 of them or simply because they don't understand how valuable they are, although the latter type is less likely to be a cheater and more likely just to be a weak player).