The majority of Muslim jurists find no harm for a woman to wear jewelry during ihram,
unless it is used for tempting or grabbing attention of men.  Dr. `Abdul-Kareem Zidan, professor of Shari`ah at Baghdad University, states the following,

It is permissible for a woman to wear any jewelry during ihram, as it has been reported by Al-Bukhari that `A’ishah (may Allah be pleased with her) did not find any harm in wearing jewellery for a muhrimah (a woman who is in the state of ihram).

In addition, it is stated in Al-Mughni by IbnQudamah that Imam Ahmad reported that Nafi` said, “Ibn `Umar’s wives and daughters used to wear jewellery and dresses dyed with safflower during ihram, and he used not to contest their action.” Imam Ahmad also reported — as mentioned in Al-Mughni — that `A’ishah elaborated that a woman can wear in ihram whatever she used to wear when she is not in state of ihram, such as silk and jewelry. Thus, the Hanbali school of thought — as far as I could conclude — allows wearing jewelry by women during ihram, as it is reported by Hanbal that Imam Ahmad said, “A muhrimah can wear jewellery and clothes dyed with safflower.”

Likewise, Malikis and Hanafis adopt the same view based on the juristic ruling that wearing jewellery is a permissible adornment, and a muhrimah is not prohibited from wearing adornments, along with the proofs that maintain the permissibility of wearing jewellery.

Shedding more light on this issue, MahmoudIsma`il, the editor of Hajj and `Umrah counsels at’s Arabic website, states,

The majority of Muslim jurists rule that wearing jewellery by women during ihram is permissible; however, we must differentiate between wearing adornments that are permissible according to the boundaries of Shari`ah and wearing jewellery with the intention of exposing it in front of men — other than the husband or mahrams— for temptation and/or grabbing attention, which is impermissible in general whether at the time of ihram or otherwise.
Wearing jewellery for unlawful goals is worse during ihram and inside the Sacred House of Allah.