It may be worth considering the following:
Zita West - have a look at her website www.zitawest.com for info. She has some books which are very useful, a relaxation CD and nutritional supplements Vitafem and Vital DHA for women, Vitamen and Vital DHA for men.
Acupuncture - It would also likely be useful for your daughter to consider acupuncture as this can help to make periods more regular and an acupuncturist can look at her diet and lifestyle and give advice. Check www.acupuncture.org.uk and also www.zitawest.com
Clearblue Fertility Monitor - using this device many help your daughter work out her fertile window each month as well as looking for signs of fertile mucous www.clearblue.info/uk/
Tests - it is worth ensuring she has appropriate tests done to see if there are any problems e.g. iron, thyroid, FSH, LH, progesterone, prolactin, testosterone etc Also perhaps a scan of her uterus would at least be a place to start. It is also worth her partner having a semen analysis to see if he is ok.
Avoiding items such as caffeine, OTC drugs etc and discuss with her GP if she or her partner are taking any prescribed drugs that interfere with fertility
Ensure she is not over or under weight.