There isn't anyway she wont get the message, if her phone is turned off, the message is stored on the fancy system and is sent to the phone when it is turned on, even with voice messages.
I can't think of any reason at all where a text would not get through, but saying that I did have a dodgy phone a few years back, I was seeing two girls, I hadn't recieved a text from either of them, bumped into a mate of mine whilst out, he asked me why I hadn't been returning his texts.
I took the battery out, put it back in and BAM, about 9 texts, progressivly getting angry at me for not responding to texts over the days from the girls I was dating.
So I guess it could happen, but what can you do? still in that scenario I got the texts even after a week, when I'd reset the phone.
Normally, i'd give it a few days and send another text, if you dont get a response then' i'd leave it.
Though also one has to keep in mind that some guys are so desperate, they expect a response almost straight away, i've had girls reply to texts a day later.
I wouldn't bombard her phone, but even then i've known girls give in after constant bombardment of texts - but these are the types of girls who dont have the for-sight to bar the number and use the constant attention as a means to award thier ego - Persistancy can work, but normally 99% of the time, it just makes you seem desperate and needy. - Also if you bombard her phone, when all she is, is busy, it will mess up the interaction, personnally, I wouldn't advise a phone text bombardment, but dont be surpised if you hear it worked in some random situation.
Also if her IL was very high, she'd probably text you, regardless if you sent a text or not.
Most of the time its not a good sign, so I dont want to give you false hope.