Surprisingly even the Arabic Wikipedia page doesn't offer anymore information than the English page, while there even doesn't exist a German one, which usually provides many information which are not in the English and usually shows different or critical views of the Arabic sources.
According to Imam a-Dhahabi's الذهبي siyar a'laam an-Nubala' سير أعلام النبلاء the mother of believers Maymunah was married twice before marrying Muhammad ().
Her first husband was Mas'ud ibn 'Amr a-Thaqafi مسعود بن عمرو الثقفي whom married her before Islam and then got separated from her, afterwards she married abu Rohm ibn Abd al-'Uzzah أبو رهم بن عبد العزى who left her as a young widow. Later she converted to islam and was the last wife of the Prophet (). She is the sister of um al-fadl the wife of al-'Abbas and therfore the maternal aunt of Khalid ibn al-Walid and ibn 'Abbas. It seems that she was around 26 years old when marrying the Prophet ().
Al-Bukhari and Muslim compiled 7 ahadith on her authority in their sahih books, one of them is only quoted by al-Bukhari and 5 only by Muslim and on the whole 13 ahadith of her have been compiled according a-Dhahabi.
A bit off-topic:
Some scholars say that the statement of verse (33:50) is addressing her:
... and a believing woman if she gives herself to the Prophet [and] if the Prophet wishes to marry her, [this is] only for you, excluding the [other] believers. ...
Imam al-Qurtobi is quoting a statement of imam az-Zamakhshari (the author of the tafisr al-Khashaaf) saying that it was said that 4 women have offered themselves for marriage to the Prophet (I've added those who quoted them):
الزمخشري : . وقيل الموهبات أربع : ميمونة بنت الحارث ، وزينب بنت خزيمة أم المساكين الأنصارية ، وأم شريك بنت جابر ، وخولة بنت حكيم
- Maymunah bint (daughter of) al-Harith (quoted by Qatadah quoting a statement of ibn 'Abbas),
- Zaynab bint Khuzaymah Um al-Masaaleen (the mother of the poors) al-Ansariya (quoted by a-Sha'abi),
- Um Shareek bint Jabir (quoted by 'Ali ibn al-Hussayn, a-Dahhaak and Muqaatil)
- and Khawlah bint Hakim (the later was quoted in a hadith by 'Aishah in sahih al-Bukhari) (quoted by 'Orwah ibn a-Zubayr).
Note that Maymunah and Zaynab were among the wives of the Prophet ().
Imam at-Tabari when quoting this verse and quoting the suggested names also quoted a narration of ibn 'Abbas with a full chain, saying that our Prophet didn't marry any of those women whom offered themselves to him.
Also read Did the Prophet(pbuh) marry his wife "Maymunah" after the revelation of Quran 33:52?